Much of the present day Grand Canal in Zhejiang and Jiangsu Provinces was constructed during the Sui Dynasty (see Figure 4 above). In CE 587, the junction of the Hong Gou canal with the Yellow River was fitted with a lock system that could regulate the water level between the river and the canal, up to a point at least, but if the difference in water levels was too great to be compensated by the canal lock, there were special slipways that allowed boats to be lowered mechanically from the river to the canal and vice-versa. These measures were put in place early during the Tang Dynasty, as indicated, but already by the year CE 600, during the reign (CE 581-604) of Emperor Wen of Sui, the canal system's overseers had to admit that the canal was so badly silt clogged (mainly with mud) that it either needed dredging, or a new canal should be dug.
In earlier times, that is, all the way back to the 6th century BCE origin of the Far-Off/ Hong Gou Canal, the canal was not directly connected – in a navigable sense – to the river, believe most scholars. Instead, the consensus belief is that the larger Yellow River boat would anchor up alongside the canal and "dock workers" would transfer the large boat's cargo to the waiting pod of smaller canal boats, in much the same way that, say, large FedEX trucks deliver their cargo to a regional terminal and it is then divided among many lesser trucks serving local routes.
The fact that a river lock system (the so-called pound lock) that could regulate the water difference between the two bodies of water, for the sake of permitting passage from the one body of water to the other, was not invented until toward the end of the 10th century (and by a Chinaman, btw – see the final section on the 100% canal) suggests that the "FedEX" solution above was most likely the actual solution in place in the very early period – then was replaced with a system whereby smaller (or medium-sized) boats could be raised/ lowered between the two bodies of water via slipways, until the pound lock was eventually invented.
Emperor Wen decided that a fresh canal was the better option, and thus the new canal, known as the Tongji Canal, was constructed, much of it diverging from the old canal, except for its first section – from Kaifeng/ Zhengzhou (on the Yellow River) southeastward to the Henan Province city of Shangqiu – where the new canal would run parallel to the old one (the old canal, after Shangqiu, passed through Xuzhou (ancient Pengcheng), Jiangsu Province, where it linked up with the Si River, which river thereafter flowed through the city of Suqian (Jiangsu) before ending at the Huai River at the city of Chuzhou (present-day Huai'an), just east of the then smallish Lake Tongzhe (and note that the present-day city of Huai'an lies about 12 kilometers north of the ancient (and present-day) city of Chuzhou, suggesting that the terrain has changed much here since the great inundations that shifted the Yellow River in CE 1194 and again in CE 1852).
The new canal, after Shangqiu, would instead continue along a direct southeasterly route through the cities of Yongcheng (Henan), Suzhou (Anhui)*(4) and Sihong (Jiangsu) before ending at the Huai River at a point roughly 25 kilometers west of Lake Hongzhe.) Thus the new Sui Dynasty Tongji Canal was 100% canal – as would the entire Grand Canal be eventually – from its orgin at Kaifeng/ Zhengzhou to its terminus at the Huai River, just west of Lake Tongzhe.
*(4) Note that the Anhui Province city of Suzhou is not to be confused with the famous lake & scholar garden city of the same name in Jiangsu Province, situated on the banks of Lake Tai, near Shanghai; the Anhui Province city of Suzhou is located some 50 kilometers, as the crow flies, south-southwest of the city of Pengcheng/ Xuzhou, Jiangsu Province. Note also that despite its new name, the Tongji Canal was often referred to, by ordinary folk, as the New Bian Canal, if they didn't call it the New Bian River – 'old habits die hard' is apparently a truth with a long history!
Other new Sui Dynasty stretches of canal were constructed more or less parallel to older canal sections, these during the reign (CE 605-617) of Emperor Yang, linking firstly the Huai River southward to the Yangtze River, then on southward to the city of Lin'an/ Hangzhou). The first stretch of this section of canal originated at a point just east of Lake Hongzhe on the Huai River near the city of Chuzhou/ Huai'an, roughly opposite the point where the old Bian Canal/ Si River terminated at the Huai River, and proceeded southward to the city of Yangzhou on the northern bank of the Yangtze River, on whose southern bank, just opposite Yangzhou, lies the present-day city of Zhenjiang.
Note that prior to the great flood of CE 1194 that shifted the Yellow River from the north side of Shandong Peninsula (green route in Figure 2) to the south side of the peninsula (red route in Figure 2) – forever altering the course of the Si River and temporarily blocking the Huai River's exit to the sea, thus causing Lake Hongzhe to permanently swell – the Huai River continued on to the sea, emptying near where the present-day river, the Guanhe, empties into the sea. (Note also that Figure 5 is pre-1194 while Figure 4 is post-1194, i.e., Figure 5 shows the original course of the Huai River all the way to its mouth at the East China Sea/ Yellow Sea). This section of Sui canal, which was parallel to the old Han Gou, or Han Canal mentioned in the introduction, would be called the Shanyang River, but would eventually be known as the Yangzhou Canal.
Of course, in the wake of the CE 1194 flooding, smaller streams were eventually cut by the amassed floodwaters around Lake Hongzhe, because freshwater will always find a way to the sea, though the bulk of the amassed waters in the immediate wake of the CE 1194 flooding that swelled Lake Hongzhe to a much greater size even than its present-day enlarged size spilled thereafter in a southerly direction along the chain of lakes – the largest of which are Baima Lake, Baoying Lake, Gaoyou Lake and Shaobo Lake, proceeding in a southerly direction (and surely expanding these lakes at the same time) – that extend southward from Lake Hongzhe to the Yangtze River. Thus the lower reaches of the Yangtze River, post-1194, carried most of the Huai River's waters as well as its own.
A view of the present-day area east of Lake Hongzhe and west of the East China Sea/ Yellow Sea reveals a myriad of small canal-like rivers – and one larger, natural river, the Guanhe – and which canal-like rivers are in fact irrigation canals, none of which existed here when the Huai River followed its normal course, emptying into the Yellow Sea east of Huai'an prior to CE 1194, though many smaller north-south running tributaries, including irrigation canals, and emptying into the pre-1194 Huai River, most likely existed here.
Between 1934 and 1937, the Subei [蘇北] Canal was dug from Lake Hongzhe to the sea (here, Su is short for "Jiangsu" (as in the province, though Su is also short for "Suzhou", the Jiangsu Province city) and bei means "north"...note that the people of northern Jiangsu Province are called the Subei and claim a separate ethnic identity, though in reality they are Han Chinese and have for centuries been poor, looked down upon cousins to the more successful Han Chinese... it was perhaps for these reasons that many Subei collaborated with the Japanese during the Second Sino-Japanese War (1937-45), which didn't exactly improve their social standing (in the wake of WWII (1939-45), which, in the Pacific theatre, was fused with the Second Sino-Japanese War, the Subei were generally despised even more because of their collaboration with the Japanese occupiers, though, it must be said, the former Premier, Zhou Enlai, was in fact a Subei), even if their traitorous action can perhaps be mitigatingly understood in the larger perspective).
The Subei Canal linked to many smaller irrigation canals and irrigation and/or drainage ditches in order to exploit the agricultural potential of the area, which had received untold amounts of rich alluvial silts due to the repeated flooding of the Yellow River. Today, this area is called the Subei Irrigation District. Note that in earlier times, much of the area slightly farther south held saltwater pools that were constantly flooded by the sea and from which salt was extracted, and a special waterway for transporting this salt, the Yunyan Canal, aka the Yan ("Salt" [塩]) Canal ran northward – still runs northward, though its course has surely also been altered over time, due to the flooding.
The Yan Canal empties into the Lin Honghe just north of the city of Lianyungang, near the coast, just where the base of the Shandong Peninsula begins. The Lin Honghe is a rather short river, or more properly, an estuary, as in the huge French estuary, the Gironde, leading from the city of Bordeaux to the sea that is also the confluence of the two super-huge rivers ("fleuve", as opposed to "rivières", in French), the Dordogne to the north and the Garonne to the south... and speaking of estuaries, the aforementioned Guanhe is itself an estuary; even larger than the Lin Honghe, it is likened to the Rhine, that is how large it is in its lower reaches. Since the Yanhe, as the Yan Canal is called on Google Maps (he [河] (sometimes anglicized as ho), just as the term jiang [江] means "river", though the term jiang has almost entirely been taken over by the Yangtze River, the Chang Jiang, or Jiang ("The River"), for short)), runs in a north-south direction, it crosses all of the aforementioned river canals that run in an easterly direction to reach the Yellow Sea east of Huai'an).
In 1938, certain key levees in Henan Province helping to contain the Yellow River were deliberately destroyed by Nationalist forces under the command of Generalissimo Chiang Kai-Shek, causing extensive flooding in the river's lower reaches and temporarily shifting the Yellow River's course directly into the Huai River again, which also caused further levee and dike destruction in the entire area east of Lake Hongzhe, more or less eliminating the just dug Subei Canal – and killing, in the process, immeasurably more Chinese people than Japanese invaders.
(No one knows, or will probably ever know, just how many Chinese people, from Kaifeng in the west to Huai'an in the east, perished in the resulting flooding, but it is estimated that anywhere between a half-million and a million Chinese people could have perished (plus quite a few Japanese occupiers, of course), directly and indirectly, as a result of this understandably defensive action to protect the motherland, an action that is reminiscent of the enormous sacrifices made by the Russian people facing, firstly, the army of Napoleon (documented in numerous historical works, but also in Tolstoy's famous novel, War and Peace) and later, the army of Hitler.)
The second stretch of the new southerly canal (south of the Yangtze River) proceeded from the present-day city of Zhenjiang (on the opposite bank of the Yangtze River from the Shanyang River section of canal ending at Yangzhou) southward to the city of Lin'an/ Hangzhou. This section of canal was called the Jiangnan (South of "The River", where nan means "south" and Jiang, as indicated above, has become a nickname for the Yangtze River) Canal, aka Jiangnan River.
Note that the reason for the "river" designation for these canal sections is that they originally followed shallow, elongated lakes and marshes (the terrain of the entire area is low-lying and marshy), and therefore these canal sections resembled more a meandering river, as indicated, than a straight canal, though they were eventually straightened out – in fact, the Si River, prior to the great flood of CE 1194, while it was connected to the Bian Canal at the city of Pengcheng/ Xuzhou, was itself straightened considerably, so as to reduce the incidence of erosion and flooding. The Jiangnan River section would eventually be called the Jiangnan Canal.
During the Tang Dynasty, this first stretch of canal, the Yangzhou Canal, was extended beyond the city of Chuzhou/ Huai'an, skirting around Lake Hongzhe in a continued arc as can be seen in Figure 4 above (the pale, non-outlined sections of canal were constructed during the Tang Dynasty, as the map's legend indicates) and linking up directly with the new Tongji Canal built during the Sui Dynasty reign of Emperor Wen. Moreover, during the Tang Dynasty, a new stretch of canal extended from the city of Bian (present-day Kaifeng) to the city of Yanzhou, some 10 kilometers west-southwest of Qufu, and also lying on the banks of the Si River.
Note that Bian, aka Bianzhou (the city had many other temporary names as well) though it would eventually be renamed Kaifeng, was a new city built in CE 781 during the Tang Dynasty on the location of Kaifeng, which ancient city had begun to blossom again during the Sui Dynasty, thanks to the creation of the new/ improved Sui Dynasty canals (the ancient city of Kaifeng was all but destroyed during the Warring States period, leaving an old city at its core).
Note also that roughly from the late Sui Dynasty through the Song Dynasty, both the city of Kaifeng/ Bian, on the Yellow River, and the city of Yangzhou, on the northern bank of the Yangtze River were major trade hubs, thanks to both the newer and older canals as well as to the two respective rivers on which they were located. In fact, the Grand Canal generated more revenue than did China's two main international ports at the time, Guangzhou, Guangdong Province, and Quanzhou, Fujian Province.
Of course there was not a lot of maritime trade at this time compared to the period after the arrival in Chinese waters of Portuguese merchant ships at the dawn of the 16th century – see the Maritime History of China to learn more – except for regional maritime trade, i.e., trade with Japan, Vietnam and the "East Indies" (Philippines, Indonesia, Malaysia, etc.), though the inland port city of Yangzhou and capital of the Sui Dynasty, situated at the northern terminus of the Jiangnan Canal section of the Grand Canal – see Figure 10 below – and also situated on the northern banks of the Yangtze River about 290 nautical miles up the Yangtze River from the river's mouth near Shanghai (which was a mere fishing village at the time) was a key port city of the ancient Maritime Silk Road.
In fact, many Arab and Persian merchants lived and worked in Yangzhou during the Tang Dynasty – so far-reaching was the Tang Dynasty's influence – until they were massacred in CE 760, en masse, during the An Shi Rebellion, aka An Lushan Rebellion, not by the rebel forces of General An Lushan, but by insurgents belonging to, or sympathetic to, the almost crushed Tang Army, though the An Lushan Rebellion had all but lost steam by that time. This tragic incident was made all the more poignant by the fact that only 4 years earlier, over 4000 Arab mercenaries had joined the side of the Tang Army against the rebel general. But in times of war, hotheaded insurgents often kill any foreigner they come across, suspecting them of having aided the enemy... viz. the fate of the Tuaregs and the black Africans in Libya's "Arab Spring" of 2011!
Another stretch of new canal was dug during the Sui Dynasty period on the north side of the Yellow River near Kaifeng (Zhengzhou), i.e., near the junction of the Yellow River with the southward running Tongji Canal. This new, very long stretch of canal, called the Yongji Canal, extended northeastward to the city of Zangzhou (present-day Cangzhou), and from there, forked out, one branch of the canal continuing in a northerly direction toward the city of Youzhou near present-day Beijing (and note that the name Youzhou was originally the name of one of 13 prefectures created by Emperor Wudi of the Western Han (BCE 206 – CE 009) Dynasty and whose capital, Ji, was situated roughly on the site of present-day Bejing) while the other branch curved in a northeasterly direction, emptying into the Bohai Sea.
Though these new stretches of canal would bring unimaginable prosperity to the country and would help to usher in one of China's most illustrious Imperial dynastic periods, namely, the subsequent Tang Dynasty, it came at a heavy price: roughly half of the 6 million workers engaged in the building of the Sui period canals died at their work, for one reason or another. Indeed, it is said that the enormous cost of the canals to China, both in terms of money and human sacrifice helped to bring down the short-lived Sui Dynasty.
On the positive side, it is claimed that the sheer number of capable public officials that the Tang Dynasty inherited from the Sui Dynasty, thanks to the army of officials necessary to oversee the building of the new canals in such a short space of time, was part of the reason behind the Tang Dynasty's success. The new canals, veritable motorways on water, helped to unify northern and southern china, creating an interdependence between the two halves, which, had this interdependence not been in place, believe some historians, China might well have been divided into a Turkic-controlled country to the north and a Han (and other) Chinese controlled country to the south. China's equivalent of America's nationwide postal system, supplemented in the western US states by the famous Pony Express, was firmly established during the Tang Dynasty.
This north-south interdependence guaranteed that even when the Turkic invaders came to control large swaths of the country to the north, they were never interested in wresting a piece of China to themselves as a separate country, but wished to wrest of the rest of the country, making it wholly theirs – which they eventually did, more or less, depending on the dynasty, during the Khitan Liao (CE 916-1125) Dynasty (or Khitan Empire, aka Kitay, and note that the old English name for China, Cathay, stems from the Khitan name for China, the Khitans being a Turkic-Mongolic tribe), the Jürchen Jin (CE 1115-1234) Dynasty, the Yuan (CE 1279-1368) Dynasty and finally, during the Qing (CE 1644-1911) Dynasty.*(5)
*(5) Note that during the period between the fall of the Jürchen Jin Dynasty (there were earlier, Han Chinese "Jin" dynasties (the Western Jin (CE 265-316) and Eastern Jin (CE 317-420) Dynasties, therefore the ethnic qualification) and the emergence of the Yuan Dynasty, founded by Kublai Khan, China was de facto ruled by the Mongol Horde originally led by Kublai Khan's grandfather, Genghis Khan. And speaking of ethnicity, the Jürchens, defeated in the first half of the 13th century by the Mongols, would rebrand themselves as the Manchus and as such would rule over China's last imperial dynasty, the Qing Dynasty.